The present invention relates to the improvement of water quality in both domestic and industrial settings, and, in particular, to an apparatus using chemical and physical means for improving water quality by inhibiting the formation of rust and scale and by filtering particulate matter from the water.
Municipal and industrial waters contain objectionable impurities, commonly referred to as hardness, which are the cause of processing problems such as scaling. Scaling is usually due to the presence of calcium and magnesium salts in the water. In both natural and industrial waters, these salts are present in various forms, including the relatively soluble calcium and magnesium bicarbonates (Ca(HCO.sub.3).sub.2 and Mg(HCO.sub.3).sub.2). Upon heating, carbon dioxide is released, precipitating calcium and magnesium carbonates (CaCO.sub.3 and MgCO.sub.3). Since the scale forms more rapidly when water is heated, the problem of scaling is particularly troublesome in water heaters and hot water systems.
The scale precipitation is predominantly on the available surface area--the inner surfaces of the pipes, coils and collecting tanks, boilers, cooling towers, shower walls, glass, sinks, etc., and upon existing layers of scale previously deposited on said surfaces. The hardness of the scale greatly promotes the attrition of faucets, valves, and pumps. Scale formation is the main problem affecting water-heating plants, in both domestic and industrial settings, causing serious operating problems and increasing utility and/or maintenance costs.
Of the many methods of water treatment, treatment with polyphosphates is potentially one of the most simple, effective and economical ways of solving the problems caused by water hardness, and is effective at temperatures up to about 80.degree. C. The action of the polyphosphate is based on the ability of polymer phosphates to be absorbed by the peripheral surfaces of calcite and magnesite crystallization nuclei, hence forming a protective film that prevents the nuclei from bonding together and thereby preventing the precipitation that causes scale deposits. Thus, even though water treated with polyphosphates retains the original hardness, the formation of damaging incrustations caused by calcareous deposits is inhibited.
Polyphosphates also work on the inner metal surfaces of the piping system, forming a very fine protective film that insulates the surfaces and protects them against corrosion.
A method and apparatus for dispensing polyphosphates in industrial applications is known. The feed water flows through a bed containing polyphosphate particles. Since the concentration of dissolved polyphosphate depends on the water flow rate, such a dosing system cannot ensure a relatively constant polyphosphate concentration. Health considerations have prompted various regulatory agencies to place an upper limit of 5 mg/liter on the polyphosphate content in municipal water, hence this method is not the most suitable for drinking water and similar domestic applications.
Industrial systems are often very sensitive to particulate matter in the water. The above method does not relate to the presence of insoluble matter in the feed water, and, in addition, the dispensing of polyphosphate results in the entrainment of polyphosphate particles which actually increases the amount of particulate matter in the water. The problem is particularly acute at high flowrates. As a result, an additional filtration unit must be installed to prevent damage to processes and to process equipment.
A method and apparatus for dispensing polyphosphates in municipal water (i.e., drinking water quality) is known. The apparatus features a suction device that operates by means of preset calibrated nozzles and exploits the so-called Venturi effect. Thus, the bulk of the feed water flows through the system without contacting the polyphosphate. Only a side stream containing small proportion of the water flows into a compartment containing the polyphosphate crystals. The residence time and contacting conditions are such that the water becomes essentially saturated with polyphosphate before rejoining the main flow of water. Since the mixing of the polyphosphate-saturated with the main flow of water is proportional to the water flow rate, the concentration of dissolved polyphosphate in the treated water discharged from the system is supposed to be fairly constant.
The utility of the known apparatus is, however, severely hampered by several characteristic problems and limitations. Small polyphosphate crystals suspended in the water in the polyphosphate compartment can be drawn into the main flow of water discharge from the system. In addition to raising the level of particulate matter in the treated water, the concentration of dissolved polyphosphate in the treated water is subject to unpredictable fluctuations and surges due to the entrainment of the polyphosphate crystals.
Moreover, as the solution leaving the polyphosphate compartment is sucked through a tiny orifice by the main flow of water being discharged from the apparatus, the presence of entrained polyphosphate crystals or other particulate matter can eventually lead to a blockage of the orifice, thereby impairing or "inhibiting" the function of the apparatus. It is also known that fine polyphosphate crystals can cause damage to the O-ring of the apparatus, resulting in water leakage and impairing efficiency.
There is therefore a need for a method and apparatus for dispensing the polyphosphate which are more reliable manner than those known heretofore, such that the quality of the product water and the performance of the apparatus are substantially improved. It would also be greatly advantageous to have an apparatus that would combine the dispensing of polyphosphate with filtration in a more compact and efficient manner than known heretofore.